How to Detect Perforations in the Air Conditioner Duct

Small leaks in central air ducts may be costing you big money.

Back in the era of low energy costs, contractors often sought to reduce building expenses on new homes by scrimping on the quality of heating and air conditioning ductwork. A substantial amount of installed residential ductwork of the past wasn’t designed or manufactured to last the life of the house, leaving today’s homeowners stuck with spiraling utility bills. Leaky, perforated ducts typically increase air conditioning costs by at least 20 percent. Fortunately, these hidden energy wasters can be detected using a number of duct diagnostic techniques.

1

Visually inspect the exterior of accessible ducts with a flashlight. Look for streaks of dust radiating from points on the surface of the ductwork that indicate perforations or pinhole leaks at that location. If the ductwork is covered or surrounded by insulation, black patches where dust emanating from perforations has stained the insulation over time is another giveaway.

2

Hold a stick of lit incense or a smoke pen in proximity to any suspected perforations in the ductwork while the system is running. Observe the smoke stream to see if it is deflected either by air from the leak or by air being drawn into the leak.

3

Watch for dust and other airborne particulates emitting from ducts when the air conditioning blower turns on. Also be aware of musty odors in living spaces. Since return ducts operate under negative pressure, perforations and other leaks in return ducts draw outside air into the ductwork rather than leaking conditioned air out. Because these ducts are routed through unconditioned areas like dirt-floored crawl spaces and dusty attics, unexplained dust and odors may indicate contaminated air sucked into the system through leaky returns.

About the Author

Gus Stephens has written about aviation, automotive and home technology for 15 years. His articles have appeared in major print outlets such as "Popular Mechanics" and "Invention & Technology." Along the way, Gus earned a Bachelor of Arts in communications. If it flies, drives or just sits on your desk and blinks, he's probably fixed it.